CRISPR/Cas9-mediated mutagenesis of per in either tim-positive or Mai179-positive neurons, by the co-expression of per^{UAS.gRNAx4.pCFD6} and Spyo\Cas9^UAS.P2 under the control of Scer\GAL4^tim.PE or Scer\GAL4^Mai179, respectively, leads to complete loss of circadian rhythmic behavior under constant darkness, although flies are still rhythmic under LD cycles.

Mutagenesis of per in Pdf-positive neurons (i.e. Scer\GAL4^P2.4.Pdf as driver of expression) leads to decreased circadian rhythmicity under constant darkness: although most individuals remain highly rhythmic, there is a decrease in morning anticipation index, but unchanged period and evening anticipation index. Under LD cycles, while the overall activity pattern and evening anticipation activity appear normal, the morning anticipation index is also reduced. There are no changes in the number of Pdf-positive neurons, as compared to controls.

Mutagenesis of per in Mai179-positive, Pdf-negative neurons (expression under the combed control of Scer\GAL4^Mai179 and Scer\GAL4^P2.4.Pdf) does not have a major effect on circadian rhythmicity under constant darkness conditions: rhythmic strength, period and morning anticipation index are unaffected, despite a decrease in evening anticipation activity. There are no obvious circadian phenotype under LD cycles.

There are no circadian phenotypes when per is mutagenized in the glia (i.e. Scer\GAL4^repo as driver of expression).